Mr. C, Mereschkowsky on Californian Diatoms. 475 
116. Nitzschia spathulata, var. hyalina, Greg. San Pedro, 
not common. [M.] 
Length 00438 mm. Endochrome composed of two plates. 
117. Nitzschia spiralis, sp. n. (Pl. V. figs. 18-20.) San 
Pedro, rather rare. [M.] 
Valve narrow, linear lanceolate, with rounded ends ; girdle- 
face narrow, linear, slightly attenuated towards the ends ; 
carinal dots elongated, not accompanied by lines, 9 in 0-01 mm. 
Frustule arcuate and twisted near one of the ends, where the 
keels cross one another, passing from one side of the frustule 
to the other. Length 0:140-0°175 mm., breadth of the 
girdle-face 0-007-0:008 mm. 
This curious form has a very different appearance according 
to the position of the frustule, as can be seen from the three 
figures, 18-20, representing the same individual—fiz, 18 
showing it in an almost quite horizontal position, fig. 19 
when slightly turned around its axis to the left, and fig. 20 
when still more turned in the same direction. In fig. 19 the 
uj per end is elevated and the lower turned down; in fig. 20 
the lower end is horizontal, while the upper one is turned 
upwards, 
The structure of this diatom can be easily 
understood if we imagine a frustule having 
the form of Niieschia sigma, in which one end 
(the inferior) has been twisted to the right 
side at an angle of about 180°: the accom- 
panying diagram shows how by such a 
process a fiustule of NV. spzralis would be 
formed; and as a consequence of this 
the lower part of the left keel ad would 
change its place from the left to the right 
side of the frustule (a c), while the other keel 
on the opposite side of the frustule would 
naturally take the opposite place, thus 
producing a crossing of both keels. The 
upper end is also slightly twisted, but in a 
much less degree than the lower one. 
The endochrome seems to be composed of 
six granules; but this requires further ex- 
amination, as the material was not in a very fresh con- 
dition. 
Cc 
118. Nitzschiella Lorenziana (var. incurva?), Grun, San 
Pedro, rather rare. [M.] 
